1. Field of the Invention
The present invention relates to a method and device for printing, and more particularly, it relates to a method and apparatus for adjusting a circumferential register in a web-fed rotary printing press having a plate cylinder with a sleeve-shaped printing plate.
2. State of the Art
Printing presses have included mechanisms for circumferentially adjusting one cylinder of the press relative to another cylinder. In web-fed rotary presses, such adjustments are usually used in conjunction with a plate cylinder to circumferentially adjust the position of the plate cylinder relative to the corresponding blanket cylinder, whereby the blanket cylinder is, for example, driven by the main drive motor of the press via a common driving shaft. In perfecting blanket-to-blanket presses, such a circumferential adjustment provides for correct registry of the images printed on both sides of the web. In multi-color presses, such a circumferential register adjustment provides for the registry of images which are printed in one printing unit with a first color and images which are printed in a second printing unit with a second color.
In prior art web-fed rotary printing presses using conventional printing plates mounted to the plate cylinders of the presses, the circumferential register adjustment of each plate cylinder is achieved by a helical spline or by a helical gear which is axially moveable on the journal of the plate cylinder as described, for example, in U.S. Pat. No. 4,709,634, the contents of which are hereby incorporated by reference in their entirety. Besides the circumferential register adjustment, the apparatus of U.S. Pat. No. 4,709,634 further allows a lateral register adjustment of the plate cylinder. However, because the axial movement of the helical gear on the journal of the plate cylinder is limited, the angle of rotation of the plate cylinder is limited. Accordingly, the circumferential register can only be adjusted within a limited range.
Known printing units use continuous printing plates in the form of sleeves which are moved onto the plate cylinder through an opening formed in one side wall of the housing of the printing unit, while the plate cylinder is cantilevered in the other side wall of the housing. In these printing units, the sleeve-shaped printing plates tend to creep on the plate cylinder body when the printing press is in operation. A printing press using sleeve-shaped printing plates is, for example, described in U.S. Pat. No. 4,913,048, the contents of which are hereby incorporated by reference in their entirety.
The creeping of the sleeve-shaped printing plates causes a constant misregistering of the respective printing unit. Accordingly, attempts have been made to eliminate the creeping of the sleeve-shaped or tubular printing plates by pinning or fixing the plate form to the respective plate cylinder body. As the sleeve-shaped printing plates are usually manufactured from light duty conventional plate material, such as aluminum, the so formed printing plates tend to break or crack when they are fixed to the plate cylinder body by pins, because the material is not strong enough to withstand the forces trying to rotate the printing plate on the plate cylinder body.